Approximately 17 million people in the United States, or 6.2% of the population, have diabetes. Diabetes is a disease in which the body does not produce or properly use insulin, a hormone that is necessary to maintain blood sugar concentration at normal levels. When insulin is not produced or properly used by the body, glucose remains in the bloodstream instead of being shuttled into cells for energy production, resulting in high blood glucose, or high “blood sugar” levels.
High blood sugar can manifest its presence through multiple symptoms, including, increased thirst, frequent urination, weight loss, increased hunger, blurred vision, irritability, tingling or numbness in the hands or feet, frequent skin, bladder, or gum infections, wounds that don't heal, and extreme, unexplained fatigue. If left untreated, diabetes can lead to death, and even diabetics undergoing doctor-supervised treatment suffer an increased death rate as compared to the average population. In 1999, approximately 450,000 deaths occurred among people with diabetes aged 25 years and older. This figure represents about 19% of all deaths in the United States in people aged 25 years and older. Overall, the risk for death among people with diabetes is about 2 times that of people without diabetes. However, the increased risk associated with diabetes is greater for younger people (3.6 times for people aged 25-44 years versus 1.5 for those aged 65-74 years) and women (2.7 times for women aged 45-64 years versus 2.0 for men in that age group).
Diabetics also face risk of multiple complications during their lifetime arising from the disease. Some of the more serious complications include: heart disease (the leading cause of death in diabetics); stroke (risk of stroke is 2 to 4 times greater for diabetics); high blood pressure (about 73% of diabetics); blindness (diabetic retinopathy causes 12,000 to 24,000 new cases each year and diabetes is the leading cause of new cases of blindness among adults 20-74 years old); kidney disease (diabetes is the leading cause of treated end stage renal disease, accounting for 43% of new cases); nervous system disease (60-70% of diabetics have mild to severe damage, such as impaired sensation of pain in the feet or hands, slowed digestion, and carpal tunnel syndrome); dental disease (almost one-third of diabetics have severe periodontal diseases); pregnancy complications (poorly controlled diabetes before conception and during the first trimester of pregnancy can cause major birth defects in 5-10% of pregnancies and spontaneous abortions in 15-20% of pregnancies); and amputations (more than 60% of non-traumatic lower-limb amputations in the United States occur among diabetics).
Diabetic neuropathic foot disease is the most common cause of amputation in the United States and arises due to coordination of several of the complications listed above. These complications often stem from the disturbance of the body's metabolism caused by the prolonged high blood sugar. The disturbance includes increased levels of serum cholesterol, triglycerides, and glucosylated hemoglobin, which lead to precipitation of the substances on the inner lining of the small blood vessels (especially capillaries) everywhere in the body, and more so in terminal blood vessels, like those found in the legs and feet. This precipitation then leads to stenosis of the blood vessels, ultimately resulting in a condition termed diabetic microangiopathy, or literally, disease of the capillaries related to diabetes. Longstanding stenosis that is widespread may decrease the total capacity of blood circulation within the body, which contributes to the high blood pressure condition referenced above. The most dangerous effect of microangiopathy, especially in the lower limbs, is occurrence of ischaemia (decreased blood supply) in the foot and leg. This condition can progress with inadequate supply of oxygen and nutrients, eventually producing devitalization and change of texture and color of the foot, starting with the big toe, which can then spread to the rest of the limb in a process called gangrene.
Diabetic patients also have increased risk of complications associated with their lower extremities, especially the feet, due to nervous system disease, as described above, that can lead to a partial or complete loss of feeling. A healthy person that starts to feel pain when subjected to continuous local pressure may shift their body or make other suitable alterations to automatically lessen the discomfort; however, patients having a sensory loss are deprived of this protection and are therefore common victims of pressure sores and open wounds that can become ulcerated. It is therefore desirable to detect the pressure points in the foot to prevent pressure sores and wounds so that a patient who might not be able to recognize existence of a pressure point inducing condition can take curative or preventative measures to eliminate or reduce the condition.
The development of protocols capable of diagnosing potential areas for the development of plantar ulcers would be of great value in decreasing and preventing diabetic foot amputation. Diabetic foot lesions are an underlying cause of hospitalization, disability, morbidity, and mortality, especially among elderly people. A protocol for early detection of plantar ulceration would avoid the need for follow-up examinations, supplementary examinations, local wound debridement, orthopedic appliances, and in some critical cases frequent hospitalization, and amputation. According to one study, it was estimated that the average cost per case of preventative care is $880, while the average cost per case for curative care is $5,227, and the average cost per case for severe lesions and amputation is $31,716 (See Van Acker, K. et al., “Cost and Resource Utilization for Prevention and Treatment of Foot Lesions in a Diabetic Foot Clinic in Belgium” Diabetic Research and Clinical Practice, 50:87-95 (2000)).
Devices are known in the prior art for indicating to persons having diminished sensation in the foot that their feet are being exposed to excessive stress conditions that could possibly lead to plantar ulcers or worse. Many of these devices include shoes, which detect excess pressure through a force sensor and signals the wearer of the existence that a threshold pressure has been reached. Examples of such devices are described in U.S. Pat. No. 5,566,479, U.S. Pat. No. 4,610,253, U.S. Pat. No. 4,647,918, and U.S. Pat. No. 5,642,096. The difficulty with such devices is that they are expensive and cumbersome to wear. Accordingly, it is desirable that there be provided a method for conveniently detecting the pressure points in the foot of a patient with diminished sensation.
A study was recently performed using interferometry for detecting plantar pressure distribution involving a laser light oriented towards a compressed plate (See Hughes, R. et al., “A Laser Plantar Pressure Sensor for the Diabetic Foot” Medical Engineering and Physics, 22:149-154 (2000)). This approach involves a pressure plate, which compresses when subjected to a load. The interferogram produced represents the pattern of pressure distribution across the plate. Such approaches as this pose an improvement over the cumbersome, expensive footwear noted above, but this method still suffers from drawbacks, such as ease of use, mass availability, and expense. Further, such methods are only useful for analyzing the bottom or sole of the foot and fails to account for pressure points on other parts of the foot. Therefore, there still remains a need for a method for detecting pressure points, especially in the foot of a patient with diminished sensation, that is effective, easy to apply, and relatively cost-effective.